As many as 27 people -- including 3 children -- had to be treated for a mixture of burns and smoke inhalation, while the man who allegedly started the fire remains under guard at hospital.

Fairfax/Ernesto Gonzalez
Police speak with a man out the back of the Commonwealth bank branch on Friday

On Friday, Country Fire Authority spokesman Paul Carrigg told reporters he understood there had been an explosion just inside the front entrance of the bank shortly after 11.30. But, he said, firefighters had not seen a container of accelerant.

"We haven't gone in search for it, it is a crime scene," he said.

"There's been apparently a flammable liquid, not sure what it was."

Police said they were unsure at this stage if there was an explosion.

UPDATE: We treated 27 people at #Springvale. 6 people have serious burns. 21 others including 3 kids have breathing problems & are stable.